1. Field of the Invention
The present invention relates to an automotive alternator mounted on a vehicle, such as a passenger car or a truck, and more particularly, to a stator winding of stator of the automotive alternator.
2. Description of the Related Art
FIG. 15 is a sectional view of a conventional automotive alternator.
The automotive alternator is constituted by a Lundell-type rotor 7 rotatably installed via a shaft 6 in a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2, and a stator 8 secured to an inner wall of the case 3 so as to cover an outer peripheral of the rotor 7.
The shaft 6 is rotatably supported by the front bracket 1 and the rear bracket 2. A pulley 4 is secured to one end of the shaft 6 to allow rotating torque of an engine to be transmitted to the shaft 6 via a belt (not shown).
Slip rings 9 are secured to the other end of the shaft 6 to supply electric current to the rotor 7, and a pair of brushes 10 are accommodated in a brush holder 11 disposed in the case 3 so that the brushes 10 slide in contact with the slip rings 9. A regulator 18 for adjusting a magnitude of ac voltage generated at the stator 8 is adhesively attached to a heat sink 17 fitted in the brush holder 11. A rectifier 12 which is electrically connected to the stator 8 and rectifies alternating current produced in the stator 8 into direct current is installed in the case 3.
The rotor 7 is constructed by a rotor coil 13 for generating magnetic flux on passage of electric current, and a pair of pole cores 20 and 21 which are provided to cover the rotor coil 13 and in which magnetic poles are formed by the magnetic flux generated by the rotor coil 13. The pair of pole cores 20 and 21 is made of iron and has a plurality of claw-shaped magnetic poles 22 and 23 arranged at equiangular pitches in a circumferential direction on outer peripheries thereof, and is secured to the shaft 6 such that the pole cores 20 and 21 oppose each other with the claw-shaped magnetic poles 22 and 23 intermeshed. Furthermore, centrifugal fans 5 are secured to both axial end surfaces of the rotor 7.
The stator 8 is constructed by a stator core 15 and a stator winding assembly 16 formed by a conductor wound around the stator core 15 and in which alternating current is produced by changes in magnetic flux from the rotor 7 as the rotor 7 rotates.
A structure of the stator winding assembly 16 will now be described in conjunction with FIG. 16 illustrating the winding.
The stator winding assembly 16 is formed by an a-phase stator winding member 16a, a b-phase stator winding member, and a c-phase stator winding member. The a-phase stator winding member 16a, the b-phase stator winding member, and the c-phase stator winding member are disposed such that they are shifted by one slot 15a from one another and are in a star connection.
FIG. 16 illustrates a winding structure of the a-phase stator winding assembly 16a; it does not illustrate winding structures of the b-phase stator winding member and the c-phase stator winding member. In FIG. 16, solid lines denote conductors connected to the rear bracket 2 (coupling portions of conductor segments, which will be discussed hereinafter), and dotted lines denote conductors connected to the front bracket 1 (coupling portions of the conductor segments which will be discussed hereinafter).
The a-phase stator winding assembly 16a is equipped with a first winding 54 and a second winding 55. The first winding 54 connected to an a-phase lead wire 100 begins at a second layer (hereinafter, a first layer from an outer peripheral side will be indicated by xe2x80x9caddress 1xe2x80x9d, a second layer by xe2x80x9caddress 2xe2x80x9d, a third layer by xe2x80x9caddress 3xe2x80x9d, and a fourth layer by xe2x80x9caddress 4xe2x80x9d) from an outer peripheral side in the slot 15a of slot number 1, and extends counterclockwise into a slot 15a at address 1 of slot number 4 from the front bracket 1 side. The first winding 54 further extends clockwise from the rear bracket 2 side into a slot 15a at address 4 of slot number 4, and exits to the front bracket 1 side. Then, the first winding 54 extends counterclockwise into a slot 15a at address 3 of slot number 4 from the front bracket 1 side, and exits to the rear bracket 2 side. Thereafter, the first winding 54 extends counterclockwise into a slot 15a at address 2 of slot number 7, and exits to the front bracket 1 side.
Thus, the conductor led out to the rear bracket 2 side at address 1, where a first layer is located in each slot 15a, enters toward the front bracket 1 at address 4, where a fourth layer is located, in a slot 15a away clockwise by three slots. Furthermore, the conductor led out to the rear bracket 2 side at address 3, where a third layer is located in each slot 15a, enters toward the front bracket 1 at address 2, where a second layer is located in a slot 15a, away by three slots counterclockwise.
Lastly, the conductor led out to the rear bracket 2 side at address 3, where a third layer is located, of slot number 34 extends counterclockwise and reaches address 1, where the first layer is located, of slot number 1, which is an end point of the first winding 54.
The end point of the first winding 54 provides a start point of the second winding 55. The second winding 55 extends clockwise and enters a slot 15a at address 2, where the second layer is located, of slot number 34 from the front bracket 1 side. Subsequently, the conductor led out from the rear bracket 2 side extends clockwise from the rear bracket 2 side, enters a slot 15a at address 3, where the third layer is located, of slot number 31, and exits to the front bracket 1 side. Then, the second winding 55 extends clockwise, enters a slot 15a at address 4 of slot number 28 from the front bracket 1 side, and exits to the rear bracket 2 side. Thereafter, the second winding 55 extends counterclockwise, enters a slot 15a at address 1 of slot number 31, and exits to the front bracket 1 side. The conductor extends clockwise and enters a slot 15a at address 2 of slot number 28.
Thus, the conductor led out to the rear bracket 2 side at address 4 in each slot 15a enters toward the front bracket 1 side at address 1 in the slot 15a located three slots away counterclockwise. Furthermore, the conductor led out to the rear bracket 2 side at address 2 in each slot 15a enters toward the front bracket 1 side at address 3 in the slot 15a located three slots away clockwise.
Lastly, the conductor led out to the front bracket 1 side at address 3 of slot number 1 extends clockwise and reaches address 4 of slot number 34, which is an end point of the second winding 55. A neutral point leader line 101 is connected to the end point.
As described above, in the a-phase stator winding member 16a, the first winding 54 connected to the a-phase lead wire 100 is wound around once counterclockwise as a whole, switching to the clockwise direction at a plurality of locations at every three slots. Then, the second winding 55 is wound around once clockwise as a whole, switching to the counterclockwise direction at a plurality of locations at every three slots. Thus, the a-phase stator winding member 16a having four turns is fabricated.
The same description of the a-phase stator winding member applies to the b-phase stator winding member and the c-phase stator winding member, so that the description will not be repeated.
The three-phase stator winding assembly 16 having the configuration set forth above is formed by joining numerous short conductor segments 50 shown in FIG. 17.
The conductor segments 50 constituting the conductor are made by forming a copper wire, which is provided with insulating coating and has a round section, into a substantially U shape. Each of the conductor segments 50 is constructed by a pair of linear portions 51a and 51b accommodated in the slot 15a, a joint portion 52 where the linear portions 51a and 51b are joined, and connecting portions 53a and 53b provided at distal ends of the linear portions 51a and 51b and which connect adjoining conductor segments 50.
A procedure for forming the a-phase stator winding member 16a by using the conductor segments 50 will now be described.
First, referring to FIG. 16, the linear portion 51a of the conductor segment 50 and the linear portion 51b, which is three slots apart, are inserted from the rear bracket 2 side at a predetermined slot number and a predetermined address. In each slot 15a, four linear portions 51a and 51b of the conductor segments 50 are arranged in a row in a radial direction.
After that, in the front bracket 1, as indicated by the dotted lines of the winding diagram of FIG. 16, the connecting portion 53a extending from the linear portion 51a and the connecting portion 53b extending from the linear portion 51b, which is three slots away, are joined to the front bracket 1 side so as to form the four-turn a-phase stator winding member 16a. As indicated by the dotted lines of FIG. 16, the connecting portions 53a of the conductor segments 50 drawn out to the front bracket 1 side from the first layer and the third layer in the slot 15a are respectively joined, at the front bracket 1 side, to the connecting portions 53b of the conductor segments 50 that are extended to the front bracket 1 side from the second layer and the fourth layer in the slot 15a that is three slots away clockwise.
The distal ends of the connecting portions 53a and 53b of the conductor segments 50 can be easily bent, and are overlapped in the radial direction substantially at a midpoint between the two slots 15a in which the conductor segments 50 are inserted. The overlapped distal ends are wrapped with clamps 29, then soldered. An inner joint portion 56 in which the distal ends of the connecting portions 53a and 53b on an inner circumferential side are joined, and an outer joint portion 57 in which the distal ends of the connecting portions 53a and 53b on an outer circumferential side are joined are disposed in a row in the radial direction as shown in FIG. 18 and FIG. 19.
In the same manner, the four-turn b-phase stator winding member and the four-turn c-phase stator winding member are fabricated, then all the three stator winding members are star-connected to make up the three-phase stator winding assembly 16.
In the automotive alternator constructed as described above, current is supplied by a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13 so as to generate magnetic flux, whereby the claw-shaped magnetic pole 22 of the pole core assembly 20 is polarized with north-seeking (N) pole, while the claw-shaped magnetic pole 23 of the pole core assembly 21 is polarized with south-seeking (S) pole. The rotating torque of the engine is transmitted to the shaft 6 via the belt and the pulley 4, thereby causing the rotor 7 to rotate. This in turn causes a rotating magnetic field to be imparted to the stator winding assembly 16, and an electromotive force is generated in the stator winding assembly 16. The alternating electromotive force is converted into direct current by means of the rectifier 12, a magnitude thereof is adjusted by the regulator 18, and the battery is recharged.
In the automotive alternator, the rotor coil 13, the stator winding assembly 16, the rectifier 12, and the regulator 18 constantly generate heat during power generation. As countermeasures for the heat produced by power generation, the front bracket 1 and the rear bracket 2 are provided with intake ports 1a, 2a and exhaust ports 1b, 2b. 
As indicated by chain lines in FIG. 15, at the rear side, the rotation of the centrifugal fan 5 causes outside air to be introduced through the intake ports 2a provided facing the heat sink 19 of the rectifier 12 and the heat sink 17 of the regulator 18, respectively, to cool the rectifier 12 and the regulator 18. Then, the air is curved in a centrifugal direction by the centrifugal fan 5 so as to cool a coil end 16b at the rear side of the stator winding assembly 16, and exhausted through the exhaust ports 2b. 
Furthermore, at the front bracket 1 side, the rotation of the centrifugal fan 5 causes outside air to be introduced through the intake ports 1a in an axial direction, then the air is curved in a centrifugal direction by the centrifugal fan 5 so as to cool a coil end 16a at the front side of the stator winding assembly 16, and exhausted to outside through the exhaust ports 1b. 
The stator winding assembly 16 generates much heat, and as it becomes hot, its output characteristic deteriorates. For this reason, the coil end 16b is positioned between the centrifugal fan 5 and the exhaust ports 1b and 2b so as to be securely cooled.
In the automotive alternator having the above construction, the inner joint portion 56 and the outer joint portion 57 are closed in the radial direction. This has been presenting a problem in that it is difficult to wrap the connecting portions 53a and 53b with the clamps 29, and solder tends to cover adjacent inner joint portions 56 or outer joint portions 57, leading to poor connecting work efficiency and a low yield.
Furthermore, since the inner joint portions 56 and the outer joint portions 57 are disposed in a row in the radial direction, it is difficult for cooling air discharged from the centrifugal fans 5 to hit the outer joint portions 57. This has been posing a problem in that temperatures of the conductor segments 50 on the outer peripheral side rise, and solder of the outer joint portion 57 melts and drips, causing short-circuit with an adjoining conductor segment 50.
There has been another problem in that the automotive alternator is mounted on the engine that incurs the severest vibrations in the automobile, so that the inner joint portions 56 and the outer joint portions 57 come in contact with each other due to the vibrations, resulting in a short circuit.
Furthermore, if the connecting portions 53a and 53b of the conductor segments 50 are joined by, for example, TIG welding instead of soldering, since the inner joint portion 56 and the outer joint portion 57 are close in the radial direction, an attempt to weld one of them frequently causes an adjoining joint portion to be welded together, presenting a problem of poor connecting work efficiency and a low yield.
In the connecting work using the TIG welding, as illustrated in FIG. 21 and FIG. 22, copper clamping jigs 40 are arranged in a straight line, distal ends of the clamping jigs 40 are butted against each other to hold the conductor segment 50, and heat is radiated by transmitting generated heat during welding via the clamping jigs 40 to heat radiating jigs 41. However, an area where the clamping jigs 40 are in contact with the conductor segment 50 is small, posing a problem in that heat is not adequately radiated at the joint portions 56 and 57 during the welding process, and the connecting portions 53a and 53b in the vicinity of the joint portions 56 and 57 incur burnt coating, making it impossible to accomplish satisfactory insulation between the conductor segments 50.
There has been still another problem in that the jigs 40 hold together the joint portions 56 and 57 arranged in a row, so that their holding performance is not reliable, leading to a likelihood of unstable TIG welding.
There has been yet another problem in that the jigs 40 are made of soft copper, and the tapered jigs 40 are abutted against each other. Therefore, the jigs 40 are easily damaged, resulting in an extremely short service life of the jigs 40.
There has been a further problem in that, if an insulating varnish is applied to the joint portions 56 and 57, then the varnish tends to be applied over the adjacent joint portions 56 and 57, clogging a passage of cooling air with consequent noises or deteriorated ability of cooling the stator winding assembly 16.
Accordingly, the present invention has been made with a view toward solving the problems described above, and it is an object thereof to provide an alternator capable of preventing a short circuit at a coil end, providing improved ability of cooling a stator winding, and reducing noises.
According to one aspect of the present invention, there is provided an alternator including a multi-phase stator winding assembly installed in a plurality of slots which extend in an axial direction of the stator core and are arranged at predetermined pitches in a circumferential direction, the multi-phase stator winding assembly comprising a coil end outside the slot on an end surface the of the stator core, the coil end having a plurality of joint portions where a distal end extending in an axial direction of a first conductor portion drawn out from an n-th layer in a slot and a distal end extending in an axial direction of a second conductor portion drawn out from an (n+1)th layer in a slot located a predetermined number of slots apart in a circumferential direction are connected, the joint portions being disposed in a plurality of rows in the circumferential direction, wherein the joint portions disposed in a radial direction are individually shifted in the circumferential direction.
In a preferred form of the alternator according to the present invention, an outer joint portion wherein a distal end of a first conductor portion extending from a first layer of a first slot and a distal end of a second conductor portion extending from a second layer in a second slot are connected, and an inner joint portion wherein a distal end of a first conductor portion extending from a third layer of the first slot and a distal end of a second conductor portion extending from a fourth layer in the second slot are connected are apart from each other by half a slot.
In an alternator according to another aspect of the present invention, a distance between an inner joint portion located on an inner peripheral side of a stator core and an end surface of the stator core is different from a distance between an outer joint portion located on an outer peripheral side of the stator core and the end surface of the stator core.
In a preferred form of the alternator in accordance with the present invention, the distal end of the first conductor portion and the distal end of the second conductor portion overlap in the radial direction to form the joint portion.
In another preferred form of the alternator, the joint portion is inclined from a diametrical line of the stator in a direction of rotation of a rotor, and the joint portion guides cooling air, which is generated by the rotation of the rotor, out of the stator core.
In still another preferred form of the alternator, there is a gap in the radial direction between an inner joint portion located on an inner peripheral side of the stator core and an outer joint portion located on an outer peripheral side of the stator core.
In yet another preferred form of the alternator, the first conductor portion and the second conductor portion form a substantially U-shaped conductor segment having leg ends bending away from each other, and the joint portions are formed by joining the leg ends by welding.
In a further preferred form of the alternator, the joint portions are coated with an insulating resin.
In a further preferred form of the alternator, the first conductor portion and the second conductor portion are formed of a continuous conductor, and are continuously connected in the joint portions.